I know I can get a client's IP address with $_SERVER['REMOTE_ADDR'], but
I was wondering if I could use PHP to get any additional information,
such as the client's geographic location (zip code would be preferable),
or even just the zip of the ISP. I have spent a lot of time looking for
a solution, but have only really found links to sites where you can
enter an IP and it will trace the info for you. I need to be able to do
it dynamically so that I can keep stats on where viewers are logging in
from (again, I just need general info, like zip code, I don't need to
pinpoint anybody). I looked at all the PHP vars displayed in phpinfo()
but didn't see anything that I thought I could use. Thanks a lot in
advance.

I know I can get a client's IP address with $_SERVER['REMOTE_ADDR'], but I was wondering if I could use PHP to get any additional information, such as the client's geographic location (zip code would be preferable), or even just the zip of the ISP.

To get the ISP's/domain registrar's address, you need to use "whois"; search
for "php whois" to get some ready to use scripts.

There are also database solutions, like GeoIP, which provide you with the
country (and sometimes additional geographical data) the IP originates from.
JW